Treatment of rayon



Patented Jan. 3, 1928.

. of artificial fibers, such as rayon.

I grams of copper for the 2,000 pounds oftion to provide a method of treating artificial gregate may be large, because of the fact that pound of rayon.

the rayon during its manufacture may be. terior of the cakes,

' nation. This object we achieve by treating 1,655,097 UNITED STATES PATENT OFFICE.

ERNEST GLADDING, 0F BUFFALO, NEW YORK, AND THOMAS E. SHARPE, OF OLD HICKORY, TENNESSEE, ASSIGNORS TO DU PON T RAYON COMPANY, INCORPORATED, OF BUFFALO, NEW YORK, A CORPORATION OF DELAWARE.

TREATMENT OF RAYON.

1T0 Drawing. Application filed March 27, 1926. Serial No. 97,981.

This invention relates to the manufacture vent the formation of It has compound. been found that the finished product shows For the purpose of illustration we-shall discoloration in the form of greenish spots describe our invention as practiced in the or streaks. The reason for this discoloration manufacture of rayon, although it is not was unknown for a long time, but we have limited thereto. The rayon may be treated discovered that it is caused by the presence with a metal cyanide in any suitable manner. of certain metal, such as copper, in the Rayon, as it comes from the-wash, may be water which is used to wash the fibers. in the form of cakes or skeins. We will first These metals may not be present 1n the describe a method of treatment of the cakes. Water in large percentages but still the ag- A bath is prepared containing sodium cyanide of a concentration of about 0.05% to about 0.2% and ammonium hydroxide of a concentration from about 0.05% to about 0.1%. In actual practice we have found that the concentrations of the above reagents may conveniently be made 0.2% and 0.1% respectively. The temperature of the bath is preferably maintained at about The cakes of rayon are moved through the bath or subjected to the action thereof by any suitable'mechanism, for example, by a conveyor which may be arranged to carry or a volatile poisonous a very great quantity of water is employed. I For example, in the manufacture of rayon by the method employing glass bobbins between 1,500 and 2,000 pounds of water are used in Washing one'pound of rayon. It is not unusual to find 0.05 parts of copper per 1,000,000 parts of water, and this propor tion, although small, is equivalent to 0.04

water which may be used in washing one The above figures are given as showing that the total amount of copper which may come in gcontact with part of the contam nation occurs on the exand, therefore, it is unnecessary to subject the cakes to the action of the cyanide for an extensive period. -We have found that one minute-will normally suiiice with the above concentrations. In this connection care must be) exercised to prevent too long a treatment with the cyas .nide, which would result in a penetration thereof into the cakes and which would then the fibers after they have been washed in require alonger period of washing to remove the water, which water is apt to contain the cyanide. the copper, with a solution of a metal cyafter passing through the cyanide bath, nide, such as sodlum cyanide or potassium thecakesof rayon are then immersed in or cyanide. A water soluble cyanide is prefersubjected to a bath of warm water at a temable. J perature approximating that of the cyanide A still further object of our invention is bath. his water should be circulating, to provide a method as set forth above and preferably, so as to insure a continual supply whlch shall be safe in operation for the of fresh water and thorough removal of the persons practicing the same. The metal cyacyanide. We have found that a period of nide which we preferably employ is sodium one minute is suflicient for the washing with cyanide, and this substance reacts with any water. traces of acid which at this stage may be The temperatures which we have indicated present in the rayon to produce hydrogen above as desirable-for both tliecyanide and cyanide or prussic acid which is very volawater baths are employed in order to hasten tile and the vapors of which are highly the rate of the chemical reactions involved pOISOIIOUS. We, therefore, incorporate in and also the rate of removal of the cyanide the bath or in the substance with which by the subsequent water washing. we treat the fibers an alkali which will pre- The efi'ectweness of the above d scribed large enough to do considerable damage. The discoloration referred to above not only detracts from the appearance of the product but also materially weakens it.

It is, therefore, the object of our invenfibers which shall remove the above contami- 40 centigrade. 1

roll the cakes through the bath. The major 4 method may be seen from the following example. A bobbin of rayon was moistened with a dilute solution of copper sulfate and then exposed to the air of the spinning room, which air was contaminated with hydrogen sulfide. After about an hour the entire cake 'was found to be covered with a very black discoloration because of the formation of copper sulfide. The cake was then placed in a bath of dilute potassium cyanide, and after several minutes it was found that the black discoloration had entirely disappeared. This was because of the formation of a soluble compound of copper with the cyanide. It is well-known that copper salts in a solution containing an excess of potassium cyanide cannot be precipitated by hydrogen sulfide. This is be-causeof the fact that there it under a is formed the compound KCu (ON) which 1on1zes almost completely as follows Copper thus being present as a part of the complexion Cu(CN) is not precipitated bv hydrogen sulfide as would be the case witi 00 per present in the form of copper ions.

lmilarly, therefore, when the rayon upon the surface of which may be found a contaminatlon in the form of a copper salt or copper in another form is treated with a metallic cyanide, ably follows, although the precise chemical reaction is unknown, because of the uncertainty as to the form in which the copper is originally present. It may occur 1n the water in the form of a soluble salt but more probably in a colloidal state, that is, in the form of insoluble particles in a very fine state of sub-division. However, regardless of the formin which the copper occurs, the above treatment effplctually removesit.

The ammonium ydroxide employed in the cyanide bath is for the purpose of preventing the formation of hydrogen cyanide or prussic acid as stated above'by reaction of the cyanide with any residual acid on the rayon. It is well-known that prussic acid is a very volatile compound. and that its vapors are highly poisonous. It is, there- 'fore, essential to prevent the escape thereof because of the consequent health hazard to the operators. The use of the ammonium hydroxlde is an example of a method of maintainin a bath slightly alkaline, in order to imme iately neutralize any residual acid which might be present in or on the cakes of rayon. Thus the formation of prussic acid is efi'ectually prevented.

When thetreatment with c anide is to be applied to the rayon in the orm of skeins, this may conveniently be done during desulfuri'ng. Rayon in the form of skems is usually esulfured and bleached b passing series of showers of so utions'of caustic'soda and sodium hypo-chlorite 1 emuch the same result probspectively. To the caustic soda solution may be added a quantity of sodium cyanlde to effect a concentration of'0.025% to 0.1%. In this treatment the ammonium hydroxide is omitted, because the caustic soda furnishes the necessary alkali. to prevent the formation of prussic acid.

While we have discussed contamlnatlons caused by copper, it is to be understood that our invention is notlimited to the removal of. such contaminations alone, but is equally applicable to the removal of contaminatlons resulting from other metals. Throughout the claims we shall employ the term metal to cover all forms in which may be found the metallic substance which causes the contamination.

We claim:

1. The method of removing a metal contamination from artificial fibers which consi sc'is in treating the fibers with a metal cyan1 e.

2. The method of removing a metal contamination from artificial fibers which consists in treating-the fibers with a water soluble metal cyanide. L

3. The method of removing a metal contamination from artificial fibers which consists in treating the fibers with sodium cyanide.

4. The method of removing a metal contamination from artificial fibers which consists in treating the fibers with a warm solution of metal cyanide."

5. The method of removing a metal contamination from artificial fibers which consists in treating the fibers with a warm solution of a water soluble metal cyanide.

6. The method of. removing a metal contamination from artificial fibers which consists in treating the fibers with a warm solution of sodium cyanide. I i

Z. The metho'd of removing a metal contamination from artificial fibers which consists in treating the fibers with a metal cyanide and an alkali. f

8. The method of removing a metal contamination from artificial fibers which consists in treating the fibers with a water solublemetal cyanide and an alkali.

I 9. The method of removing a metal contamination from artificial fibers which consists in treating the fibers with sodium cya- 12. The method of removing a metal consolution to which is added a water soluble tamination from artificial fibers which conmetal cyanide. sists in treating the fibers with a desulfuring In testimony whereof, we have afiixed our 10 solution to which is added a metal cyanide. signatures to this specification. 5 13. The method of removing a metal contamination from artificial fibers which CuIl- ERNEST K. GLADDING. sists in treating the fibers with a desulfuring THOMAS E. SHARPE. 

